1. Field of the Invention
The present invention relates to a sole, and a shoe and a sandal including the same, and more particularly, it relates to a sole having a plurality of bottom surfaces, and a shoe and a sandal including the same.
2. Description of the Prior Art
In general, normal articular movements and muscular activity enable natural action of a human body. It is well known that hypofunction results when normal articular movements are limited or muscles are not used.
An average man of today, generally protecting his feet with shoes and walking on a flat and hard paved road, is restrained from natural pedal motion. Consequently, the pedal function deteriorates and the muscles of lower extremities get weak with no requirement for adaptability to uneven ground. While exercise such as jogging or walking is necessary in order to prevent the lower half of the body from weakening and develop physical strength, most people cannot take time for exercise.
An infant naturally stands or walks on tiptoe or with the heels in the process of development. A general infant naturally takes such action in the process of growth/development in an untaught manner. The infant acquires new functions one after another by repeating such natural action. The motion observed in such action of.the infant is classified into two elements, i.e., acquired "natural motion" and "specific motion" for training the same.
In practice, a patient suffering from paralysis of the lower half of the body as an after effect of cerebral apoplexy or the like and having difficulty in walking starts moving his ankles similarly to the process of development of an infant as functional training. Then he trains for standing and thereafter for walking so that he can walk on an uneven road in a well-balanced manner. In the functional training, the patient generally makes a series of movements he has naturally made in the process of development as described above.
Thus, it is conceivable that a sole with which everybody can naturally prevent his foot from weakening or recover the pedal function in daily life with reference to the movements in the process of human growthdevelopment is preferable.
A shoe must be so developed as not to hinder the foot of a person wearing the same from natural motion, to compensate for weak points of the foot resulting from anatomical characteristics and to add new advantages. Such features are obtained not by mere trial and error or experience but by detailed scientific study on feet and shoes. Combination of materials, combination of structures or to what portion of the shoe (what portion of the foot) the combination is applied is an important factor, which can never be obtained by trial and error with no theory.
Theory in development of a shoe is now described with reference to three points, i.e., "natural motion of a foot", "movements of joints" and "weak points of a foot and limitation of articular excursions".
First, "natural motion of a foot" is described. Important natural motion of a foot includes motion of gripping a projecting portion of the ground with the foot in a standing position as shown in FIG. 15 and "aori" motion in barefooted walking as shown in FIG. 16. Further, it is important to absorb a shock and enlarge the surface touching the ground by deformation of a fatty layer of the heel when the touching the ground with the heel as shown in FIG. 17, although this cannot be regarded as motion. Particularly when obliquely touching the ground with the heel for turning around or walking on a curve as shown in FIG. 18, the deforming fatty layer most effectively absorbs a shock and enlarges the surface touching the ground.
As disclosed in "Talk on Feet" by Shiro Kondo, Iwanami Shinsho, 1982 (referred to as literature 1), "aori" motion in barefooted walking is a way of walking by rotating the foot inward for reducing energy consumption in walking thereby enabling long-sustained walking. In such aori motion, the heel touches the ground, the fibular margin of the foot touches the ground, the overall bottom of the foot touches the ground, the heel separates from the ground, the tiptoe supports the body weight and the foot kicks the ground while making motion from supination to pronation when touching the ground with the heel and then touching the ground with the overall bottom of the foot and making motion from pronation to supination when touching the ground with the overall bottom of the foot and then kicking the ground.
"Movements of joints" are now described. Principal joints concerned when a human stands, walks or runs are the hip joint, the knee joint, the ankle and the joints of the foot. According to "Kapandji Physiology of Joints" by Kapandji, Japanese translation supervised by Hideo Ogishima, Ishiyaku Shuppan, 1986 (referred to as literature 2), pp. 204 to 205, among these joints, the ankle and the joints of the foot coupling the leg and the foot so work that the human can stand, walk or run in conformity to inclination or unevenness of the ground.
The ankle (talocrural articulation), which is most important among the joints present in the metapodium, adjusts motion between the foot and the leg by the sagittal plane, and this motion is important for walking on level or uneven ground. On a basic position shown in FIG. 19A, the bottom of the foot is perpendicular to the long axis of the leg. Motion of the ankle includes dorsiflexion shown in FIG. 19B, plantar flexion shown in FIG. 19C, adduction shown in FIG. 20A, abduction shown in FIG. 20B, supination shown in FIG. 21A, pronation shown in FIG. 21B, and incycloduction and excycloduction shown in FIGS. 22A and 22B combining the same. The normal excursion of the ankle varies with scholars. While the inventor has heretofore regarded the normal excursion of the ankle as 20 degrees in supination and 40 degrees in pronation, it is conceivably proper in shoemaking to take the idea that the normal excursion is 20 degrees in supination and 30 degrees in pronation with individual variation of 20 degrees and 10 degrees respectively as described in literature 2, pp. 134 to 135.
While the foot includes a large number of complicated joints, important joints are the talocalcaneal joint (joint between the ankle bone and the calcaneus), the transverse tarsal joint (at the tarsal center), the tarsometatarsal joint, the cuboidal navicular joint and the cuneonavicular joint, and literature 2 describes in p. 148 that these joints have two functions.
The first function is to move the foot in relation to two axes other than the sagittal plane to correctly direct the bottom of the foot to the ground regardless of the position of the leg or inclination of the ground. In other words, the ankle adjusts motion on the sagittal plane, i.e., supination and pronation of the ankle.
The second function is to change the shape and the curve of the arch of the foot so that the foot properly fits unevenness of the ground. Thus, a buffer is inserted between the ground and the loaded foot, thereby making the stance phase flexible in walking.
"Weak points of a foot and limitation of articular excursions" is described. First, fatigue and trouble of the foot following pronation are described. These are disclosed in "The Shoe and Foot New Medical Study" by Tadao Ishizuka, Kanahara Shuppan, 1996 (referred to as literature 3), pp. 42 to 44.
FIG. 23 illustrates a line of a movement of the body weight as viewed from behind. Referring to FIG. 23, a calcaneus 101 is not linked on the same position as a tibia 102 but located outside the tibia 102, i.e., on a position closer to a fibula 104. Therefore, the body weight passes through the center of the tibia 102, moves outward on the ankle bone and reaches the calcaneus 101. However, the gravitational line straightly reaches the ankle bone downward from the tibia 102, and hence force of pronation acts on the calcaneus 101. Further, the arch slightly lowers upon application of a load, and hence the foot slightly pronates in walking as a matter of course. When walking or continuously standing for a long time, however, the foot is continuously loaded, to result in trouble as pes pronatus. This leads to tension of the muscle of the posterior part of the leg, pain on the ankle or the knee, tension of the Achilles' tendon or chronic pain on the overall foot.
In relation to this, FIG. 24 shows a sustentaculum (sustentaculum tali) 106, which is an important portion connecting the calcaneus 101 and an ankle bone 108, supporting most part of pressure applied to the overall body and distributing force to the heel and the propodium. This sustentaculum 106 serves as the prime mover for motion such as standing, walking, running or jumping. The sustentaculum 106 having a normal arch is stabilized on a position correctly at 90 degrees with respect to the long axis of the foot. The ankle bone 108, securely placed on the sustentaculum 106, is not tightly fixed onto a plane but consistently placed on a loose curve. Due to this structure, the calcaneus 101 swinging vertically, rotating or swinging transversely under the ankle bone 108 (see literature 2, pp. 158 to 159) is regarded as the portion most fatigued when walking.
Particularly when a woman wears high heels or the like for a long time, the heel and the toe support the body weight and hence the unsupported sustentaculum 106 is remarkably fatigued. Further, the sustentaculum 106 is inclined inward and cannot keep the position of 90 degrees due to lowering of the arch or pes pronatos, to cause tension on the ligament and inflame the talocalcanean joint, the talonavicular joint, the calcaneocuboid joint or the like (refer to literature 3, pp. 44 to 46).
As shown in FIG. 24, the sustentaculum 106 is located on a relative position of 22 to 28% from the heel in consideration of individual variation assuming that the distance between the heel (0%) and the toe is 100%.
When the body weight is put on a bare foot, a tuberosity of fifth metatarsal 112 comes into close contact with the ground to form a base for firmly supporting the body weight as shown in FIG. 25, while an articular surface 113 of a cuboid bone 110 comes into close contact with the tuberosity of fifth metatarsal 112 as shown in FIG. 26. When wearing a low heel 150 as shown in FIG. 27, however, the tuberosity of fifth metatarsal 112 separates from the ground not to function as the base for supporting the body weight, and the joint between the tuberosity of fifth metatarsal 112, the cuboid bone 110 and the ankle bone slightly opens. When wearing a high heel 151 as shown in FIG. 28, on the other hand, the joint between the tuberosity of fifth metatarsal 112, the cuboid bone 110 and the ankle bone largely opens to result in chronic tension on the ligament, leading to ache around the foot (refer to literature 3, pp. 46 to 47).
The tuberosity of fifth metatarsal 112 is located on a relative position of 35% to 41% in consideration of individual variation, assuming that the heel is 0% and the toe is 100%.
Limitation of the dorsiflexion excursion of the ankle is now described. FIGS. 29 and 30 illustrate changes of excursions of dorsiflexion and plantar flexion of the ankle with aging disclosed in "The Range of Joint Motions of the Extremities in Healthy Japanese People--The Difference According to the Age--" by Hideo Watanabe and three others, Nihon Seikei Geka Gakkai Zasshi, Vol. 53, No. 3, Mar. 25, 1979 (referred to as literature 4). Referring to FIG. 29 showing variation of dorsiflexion excursion with age, the dorsiflexion excursion reduces with aging after the age of 20. Referring to FIG. 30 showing variation of plantar flexion excursion with aging, the plantar flexion excursion remains substantially unchanged after the age of 20 up to the age of 60.
One of the factors limiting the dorsiflexion excursion of the ankle with aging resides in that the heel of a conventional shoe is on a position higher than that of the toe and the ankle of the foot of a person wearing such a shoe is regularly kept in the state of plantar flexion. As pointed out in literature 3, the position of the heel of a current heeled shoe is higher than that of the toe to bring a negative effect on the foot, change the balance of the foot regardless of the way of walking and break the mechanism of the foot naturally supporting the body.
Another factor resides in that an ordinary human often going up the stairs seldom goes up a slope on foot in ordinary environment although the ankle performs dorsiflexion when going up a slope on foot. Such limitation of dorsiflexion of the ankle results in stumbling and falling.
On the basis of the aforementioned theory in development of shoes, the inventor has proposed the structure of a sole enabling "aori" motion in Japanese Patent No. 2,791,658. More specifically, this sole enables aori motion by reducing the thickness of the outer side of a third bottom surface as compared with that of the inner side while increasing the width of the outer side as compared with the inner side for providing inclination from the inner side toward the outer side.
However, the aforementioned proposed sole, forcibly making the foot of a person wearing this sole to touch the ground with the outer side by reducing the thickness of the outer side of the third bottom surface as compared with that of the inner side, is insufficient in absorption of a shock applied when touching the ground with the outer side. Therefore, it is difficult to more smoothly perform aori motion with this sole.
In the aforementioned proposed sole, further, no consideration is made on shock absorption and enlargement of the surface touching the ground by deformation of the fatty layer of the heel and balance of plantar flexion and dorsiflexion of the ankle.